Magnetic transitions in a heavy-fermion antiferromagnet U2Zn17 at high pressure.

Pressure-dependent electrical resistivity and ac-calorimetry measurements on single crystals of the heavy-fermion antiferromagnet U(2)Zn(17) at pressures to 5.5 GPa reveal that the low temperature magnetic order changes above ∼3 GPa. The Neél temperature (T(N) = 9.7 K at ambient pressure) decreases slowly for pressures below 3 GPa, but above this pressure a new magnetic state develops at T(M)≈8.7 K. This magnetic phase becomes more stable with pressure increase (dT(M)/dP = 1 K GPa(-1), T(M) = 10.5 K at 5.3 GPa). The heavy-electron state in U(2)Zn(17) is robust against pressure--the electronic specific heat coefficient γ≈0.4 J mol(-1) K(-2) is nearly pressure independent for both magnetic phases. Magnetic ac-susceptibility measurements show that the pressure-induced state is not ferromagnetic.